Hybrid vehicles of the type having both a combustion engine and a battery-powered electric motor provide greater fuel efficiency or gas mileage than conventional vehicles. Typically, the hybrid vehicle is a compact or light-weight passenger sedan, with the capability of re-charging the on-board battery from the rotation of the axle or wheel. In some models, the vehicle may also be charged from an electrical outlet, in the owner's garage for example. The performance of such a hybrid vehicle depends very highly on the vehicle weight. For optimum vehicle performance, the weight is minimized. However, certain components are required that are either costly or heavy, including the engine, transmission, electric motor/generator components, engine throttle/fuel injection controls. These components also greatly affect the weight and the cost of the hybrid vehicle.
Among various costly items, a hybrid vehicle requires a complex control system for managing the combustion engine throttle, the power delivered to the electric motors and the charging of the battery. The control system must coordinate the engine throttle, the electric motor drive power and the battery-charging current simultaneously in response to changing acceleration and deceleration commands from the driver. The need for the costly or heavy components, including the combustion engine, automatic transmission, electric motor(s), and a complex controller limits the degree to which the vehicle efficiency can be improved or its cost reduced. The controller governs the throttling of the engine, and simultaneously manages the power demand on the electric motors whenever needed to supplement torque if the engine capability is exceeded by the demands to the driver. The controller typically throttles the engine so as to optimize its efficiency, by maintaining its torque output above a predetermined fraction of maximum torque, for example. At the same time, the controller must determine the amount of supplementary power from the electric motors required to meet power demands. Such a controller is complex and is relatively costly.